Nanoparticulate encapsulation barrier stack

ABSTRACT

A barrier stack for encapsulating a moisture and/or oxygen sensitive electronic device is provided. The barrier stack comprises a multilayer film having at least one barrier layer having low moisture and/or oxygen permeability, and at least one sealing layer arranged to be in contact with a surface of the barrier layer, wherein the sealing material comprises reactive nanoparticles capable of interacting with moisture and/or oxygen, thereby retarding the permeation of moisture and/or oxygen through defects present in the barrier layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National Stage application of PCT/SG2006/000334,filed Nov. 6, 2006.

The present invention relates generally to the field of encapsulationbarrier stacks, and more particularly to encapsulation barrier stackscomprising reactive nanoparticles.

BACKGROUND OF THE INVENTION

Organic Light Emitting Displays (OLEDs) are widely seen as the nextgeneration display technology that will come to replace existing displaytechnology. Amongst the various challenges to be dealt with in thedevelopment of OLEDS, effective encapsulation remains one of the mostsignificant.

One commonly known problem with OLED structures and other oxygen and/ormoisture sensitive electroluminescent devices is that they degraderapidly under atmospheric conditions. In order to protect them fromdegradation, various types of encapsulation have been used to isolatethe electroluminescent devices from the environment. It is estimatedthat for an OLED to achieve reliable performance with a lifetimeexceeding 10,000 hours, the encapsulation around the reactiveelectroluminescent material should have an oxygen transmission rate(OTR) less than about 5 to 10 cc/m²/day and a water vapor transmissionrate (WVTR) of less than about 10⁻⁵ g/m²/day at 39° C. and 95% RH. Thetechnical challenges brought about by these stringent requirements havedriven constant developments in encapsulation technology over the years.

Conventional encapsulation structures comprise a substrate on which theelectroluminescent device is formed, and a covering structure whichseals the electroluminescent device against the substrate. In certaintypes of electronics applications, such as hard disk drives, oneapproach in improving the barrier properties of an encapsulation is toutilise thick, gas impermeable encapsulation structures. However, thisapproach is not suitable for applications such as OLEDs or solar cellsin which opacity is a requirement and the quality of light transmittedthrough the encapsulation must be maintained.

Recent developments in OLED technology has seen the rise of flexibleOLEDs which require that the encapsulation structures are flexible,thereby making it more apparent that encapsulation technology has notkept pace with developments in OLED technology. The substrate for aflexible OLED should ideally combine the gas barrier properties,chemical resistance and surface properties of glass with theflexibility, toughness and processability of conventional plastics.Transparent polymers were used to form various parts of an encapsulationstructure because they were inexpensive and easily processed. However,due to their permeability to moisture and oxygen, encapsulationstructures formed from polymers alone are nowadays considered to beinadequate for achieving low permeation rates as the required standardfor oxygen and water vapor impermeability are orders of magnitude lowerthan what is achievable with the best polymer substrates using today'sstate of the art in industrial polymer technology.

More recently, barrier laminates derived from certain types of inorganicmaterials were found to have better barrier properties than polymericbarrier laminates. Metals such as aluminium are now used as barriermaterials (e.g. aluminium foils) for packaging food substances andpharmaceutical drugs. Despite possessing improved barrier properties, ithas been found that the performance of inorganic barrier laminates isstill limited by inherent structural defects. Recent studies have shownthat structural defects such as pinholes, cracks, grain boundaries,etc., allows oxygen and moisture to permeate over time, leading topoorer than expected barrier performance. It is difficult to controlfabrication to such an extent that defects are completely eradicatedbecause such defects are randomly formed, independent of the method offabrication.

One approach that has been used to overcome the problems of poor barrierproperties in polymer barrier stacks and the problems in formingdefect-free inorganic barrier layers is to stack multiple polymer/metaloxide layers together to form a barrier stack. It has been found thatcombining polymer layers with metal oxide layers enables the defects ofone polymer/barrier oxide stack to be decoupled from the nextpolymer/barrier oxide stack, thereby slowing down the propagation ofoxygen/moisture from one inorganic layer to the next.

Vitex Inc. discloses in U.S. Pat. No. 6,866,901 a multilayer barrierstacks comprising multiple sputter-deposited aluminium oxide inorganiclayers separated by polymer multilayers (PML) comprising organicpolymers. This multi-layer barrier stack design is based on theprinciple of decoupling the defects of two successive barrier oxidelayers in the multilayer barrier stack. A recent modelling studysuggests that defect decoupling due to the organic/inorganic multilayersforces a tortuous path for moisture and oxygen diffusion, thus reducingthe permeation rate by several orders of magnitude.

Despite this development, a large number of thick barrier oxide andpolymer interlayers are needed in order to achieve ultra high barrierproperties of better than 10⁻⁶ g/m²/day, or even better levels of 10⁻⁶g/m²/day. Variations in overall barrier performance still arise due tofactors such as whether the pinholes in one layer are lined up with thedefects in the other layers. Other limitations of the multilayer stackapproach is that it suffers from poor adhesion and frequent delaminationoccurs, especially during the thermal cycles of the OLED fabricationprocesses, since the inorganic and organic layers have sharp interfaceswith weak bonding structure due to nature of the sputter deposition andPML formation processes. It also results in thick panels with poortransmission qualities and which cracks easily.

HELICON Research, Inc. discloses in US Patent Application No.2005/0051763 an organic/inorganic nanocomposite structure formed byinfiltration of a porous inorganic layer by an organic material. Thecomposite structure is produced by vacuum deposition techniques. Incontrast with the aforementioned techniques, this document teaches thefabrication of porous inorganic barrier layer onto plastic substrate andthen depositing organic material in the barrier layer such that itinfiltrates the porous inorganic material to form a continuous layer.

General Electric Inc. discloses in EP 1 164 644 a barrier system whichutilizes the high temperature resistance and high clarity of transparentLexan™ film properties to enable a 125-micron-thick substrate towithstand the heat involved in OLED fabrication and to allow optimallight transmission from the device. The barrier coating comprisessilicon oxide compounds which are applied onto the substrate usingplasma enhanced chemical vapour deposition. The barrier coating preventsdegradation of the device from oxygen, moisture, chemicals, andelectronic conductivity while promoting light transmission.Additionally, nanoparticles reactive with moisture are incorporated intothe base substrate.

Nanocomposite barrier materials comprising mineral clay nanoparticlesdistributed in a polymeric binder have been developed for use in foodpackaging materials. For example, U.S. Pat. No. 5,916,685 discloses amultilayer barrier laminate comprising an exterior polymeric layercontaining non-reactive clay nanoparticles in the quantity of about 0.1to 10% by weight of a polymer layer in which it is distributed. Thepolymer layer is arranged on an inner metal oxide barrier layer. Thebarrier laminate achieves a water vapour transmission rate of about 0.61g/m²/day over a 24 hr period, and is clearly unsuitable for OLEDencapsulation.

Accordingly, limitations in the barrier performance of existingencapsulation structures still exists. An object of the presentinvention is to provide an alternative barrier stack that has improvedbarrier properties and is inexpensively fabricated.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, an encapsulationbarrier stack capable of encapsulating a moisture and/or oxygensensitive article is provided, comprising:

a multilayer film having at least one barrier layer having low moistureand/or oxygen permeability, and at least one sealing layer arranged tobe in contact with a surface of the at least one barrier layer, therebycovering defects present in the barrier layer, wherein the at least onesealing layer comprises reactive nanoparticles capable of interactingwith moisture and/or oxygen to retard the permeation of moisture and/oroxygen through the defects present in the barrier layer.

According to another aspect of the invention, an electronic devicecomprising a moisture and/or oxygen sensitive reactive component isprovided in which said reactive component is arranged within anencapsulation barrier stack according to the first aspect of theinvention.

The invention is also directed to a method for the manufacture of anencapsulation barrier stack according to the first aspect of theinvention, comprising:

forming at least one barrier layer and at least one sealing layer inalternating sequence, wherein forming the at least one sealing layercomprises mixing a polymerisable compound with a nanoparticle dispersionto form a sealing mixture, and polymerising the sealing mixture over theat least one barrier layer under vacuum.

The present invention is based on the finding that coupling a sealinglayer which comprises reactive nanoparticles to an inorganic barrierlayer can effectively reduce the rate at which moisture or oxygenpermeates the barrier layer. Rather than seeking to improve existingbarrier layer fabrication methods, the present invention utilisesreactive nanoparticles that either adsorbs or chemically react withmoisture and/or oxygen to plug the defects present in the barrier layer.This approach of dealing with the problem of defects typically presentin metal oxide barrier layers can be implemented inexpensively giventhat it can be integrated with existing processes. Apart from theimprovement in barrier properties, the inventors have also found thatthe use of sealing layers containing nanoparticles result in improvedlamination between barrier layers due to the high surface roughnessprovided by the nanoparticles. For stringent applications, a pluralityof barrier films with intervening polymeric interlayers containingreactive nanoparticles may be used to achieve a high level of gasimpermeability. This solution to the problem of defects in inorganicbarrier films is supported by two-dimensional finite element modelling,which has shown that a key requirement for achieving ultra high barrierperformance is that the organic defect decoupling layer thickness issmaller than the typical offset distance between the defects in barrierlayers.

In accordance with the above findings, the encapsulation barrier stackof the invention comprises a multilayer film having at least one barrierlayer with low gas permeability, and at least one sealing layer arrangedto be in contact with a surface of the barrier layer. The sealing layercomprises reactive nanoparticles that can interact with moisture and/oroxygen, thereby retarding their permeation through the barrier stack viadefects present in the barrier layer.

“Defects” in the barrier layer refer to structural defects, such aspits, pinholes, microcracks and grain boundary. Such structural defectsare known to exist in all types of barrier layers that are fabricatedfrom deposition processes from which barrier layers are typicallyproduced, such as chemical vapour deposition, as well as roll-to-rollprocesses. Gases can permeate these defects, thereby leading to poorbarrier properties (see Mat. Res. Soc. Symp. Proc. Vol. 763, 2003,B6.10.1-B610.6).

“Reactive” nanoparticles refer to nanoparticles capable of interactingwith moisture and/or oxygen, either by way of chemical reaction (e.g.hydrolysis or oxidation), or through physical or physico-chemicalinteraction (e.g. capillary action, adsorption, hydrophilic attraction,or any other non-covalent interaction between the nanoparticles andwater/oxygen). Reactive nanoparticles may comprise or consist of metalswhich are reactive towards water and/or oxygen, i.e. metals which areabove hydrogen in the reactivity series, including metals from Group 2to 14 (IUPAC) may be used. Some preferred metals include those fromGroups 2, 4, 10, 12, 13 and 14. For example, these metals may beselected from Al, Mg, Ba and Ca. Reactive transition metals may also beused, including Ti, Zn, Sn, Ni, and Fe for instance.

Other than metals, reactive nanoparticles may also include or consist ofcertain metal oxides which are capable of interacting with moistureand/or oxygen may also be used, including TiO₂, Al₂O₃, ZrO₂, ZnO, BaO,SrO, CaO and MgO, VO₂, CrO₂, MoO₂, and LiMn₂O₄. In certain embodiments,the metal oxide may comprise a transparent conductive metal oxideselected from the group consisting of cadmium stannate (Cd₂SnO₄),cadmium indate (CdIn₂O₄), zinc stannate (Zn₂SnO₄ and ZnSnO₃), and zincindium oxide (Zn₂In₂O₅).

In this conjunction, it is evident for a person skilled in the art thatreactivity may depend on the size of the used material (see J. Phys.Chem. Solids 66 (2005) 546-550). For example, Al₂O₃ and TiO₂ arereactive towards moisture in the form of nanoparticles but areunreactive (or reactive only to a very small extent) in the (continuous)bulk phase, such as a microscale or millimeter scale barrier layer whichis beyond the nanoscale dimension of several nanometers to severalhundred nanometers typically associated with nanoparticles. Accordingly,using Al₂O₃ and TiO₂ as illustrative examples, Al₂O₃ and TiO₂nanoparticles are considered to be reactive towards moisture, whereasAl₂O₃ and TiO₂ bulk layers are passive barrier layers having lowreactivity towards moisture. In general, reactive metal or metal oxidenanoparticles, for example Al₂O₃, TiO₂ or ZnO nanoparticles, may bepresent in suitable colloidal dispersions for the preservation ofreactivity and may be synthesised via any conventional or proprietarymethod such as the NanoArc® method from Nanophase TechnologiesCorporation.

Apart from metals and metal oxides, reactive nanoparticles in thesealing layer may also comprise or consist of carbon nanoparticles, suchas carbon nanotubes, nanoribbons, nanofibres and any regular orirregular shaped carbon particles with nanoscale dimensions. For carbonnanotubes, single-walled or multi-walled carbon nanotubes may be used.In a study carried out by the present inventors, it was found thatcarbon nanotubes (CNTs) can serve as a desiccant. Carbon nanotubes canbe wetted by low surface tension liquids via capillary action,particularly liquids whose surface tension does not exceed about 200Nm<“1> (Nature, page 802, Vol. 412, 2001). In principle, this would meanthat water molecules can be drawn into open-ended carbon nanotubes bycapillary suction. It is suggested that water molecules may formquasi-one-dimensional structures within carbon nanotubes, therebyhelping to absorb and retain a small volume of oxygen and watermolecules. While the quantity of carbon nanotubes may be maximised formaximum moisture and/or oxygen absorption, the inventors have found thatin practice lower amounts are also suitable. For example, carbonnanotubes may be used in low quantities of about 0.01% to 10% by weightof the nanoparticles present. Higher concentrations of carbon nanotubesmay also be used, but with a corresponding decrease in the transparencyof the encapsulation barrier stack.

In one embodiment, inert nanoparticles are included in the sealing layerand used in conjunction with reactive nanoparticles. As used herein,“inert nanoparticles” refer to nanoparticles which do not interact atall with moisture and/or oxygen, or which react to a small extent ascompared to reactive nanoparticles. Such nanoparticles may be includedinto the sealing layer to obstruct the permeation of oxygen and/ormoisture through the sealing layer. Examples of inert particles includenanoclays as described in U.S. Pat. No. 5,916,685. Such nanoparticlesserve to plug the defects in the barrier layer, thereby obstructing thepath through which permeation takes place, or at least reducing thedefect cross-sectional area, thus rendering permeation pathways by whichwater vapour or oxygen diffuses through the defect much more tortuous,thus leading to longer permeation time before the barrier layer isbreached and thereby improving barrier properties.

Other suitable materials for inert nanoparticles may also includeunreactive metals such as copper, platinum, gold and silver; minerals orclays such as silica, wollastonite, mullite, monmorillonite; rare earthelements, silicate glass, fluorosilicate glass, fluoroborosilicateglass, aluminosilicate glass, calcium silicate glass, calcium aluminumsilicate glass, calcium aluminum fluorosilicate glass, titanium carbide,zirconium carbide, zirconium nitride, silicon carbide, or siliconnitride, metal sulfides, and a mixture or combination thereof.Encapsulation barrier stacks which comprise sealing layers having onlyinert nanoparticles, such as nanoclay particles, do not belong to theinvention.

Without wishing to be bound by theory, the inventors believe that strongbarrier properties can be achieved by using a combination of differenttypes of nanoparticles. By studying the absorption/reactioncharacteristics of different types of nanoparticles, it is possible toselect a combination of nanoparticles which compliment each other toachieve stronger barrier effects than with a single type of material.For example, different types of reactive nanoparticles may be used inthe sealing layer, or a combination of reactive and inert nanoparticlesmay be used.

In accordance with the above, the sealing layer may comprise acombination of carbon nanotubes and metal and/or metal oxidenanoparticles. One exemplary embodiment would be the combination ofTiO₂/Al₂O₃ nanoparticles with carbon nanotubes. Any range ofquantitative ratios may be used and optimised accordingly using regularexperimentation. In an exemplary embodiment, the quantity of metal oxidenanoparticles present is between 500 to 15000 times (by weight) thequantity of carbon nanotubes. For oxides of metals having low atomicweight, lower ratios can be used. For example, TiO₂ nanoparticles can beused in combination with carbon nanotubes, with the weight ratio ofcarbon nanotubes to TiO₂ being between about 1:10 to about 1:5, but notlimited thereto.

The encapsulation barrier stack of the invention may be used toencapsulate any type of moisture and/or oxygen sensitive article, suchas electronic devices, drugs, foods, and reactive materials, forexample. For encapsulating electroluminescent devices, the quality oflight transmitted through the encapsulation barrier stack isparticularly important. Thus, when the encapsulation barrier stack isused as a cover substrate over a top-emitting OLED, or when theencapsulation layer is designed for TOLED or see-through displays, theencapsulation barrier stack should not cause the quality of lighttransmitted by the electroluminescent device to be substantiallydegraded.

Based on the above requirement, the size of the particles may be chosenin such a way that optical transparency is maintained. In oneembodiment, the sealing layer comprises nanoparticles having an averagesize of less than ½, or more preferably less than ⅕, the characteristicwavelength of light produced by the electroluminescent electroniccomponent. In this context, the characteristic wavelength is defined asthe wavelength at which the peak intensity of the light spectrum that isproduced by the electroluminescent device. For electroluminescentdevices emitting visible light, this design requirement translates intonanoparticles having a dimension of less than about 350 nm, or morepreferably less than 200 nm.

As the random packing density of nanoparticles in the defects of thebarrier layer is determined by the shape and size distribution of thenanoparticles, it is advantageous to use nanoparticles of differentshapes and sizes to precisely control the sealing of defects of thebarrier oxide layer. The nanoparticles may be present in one uniformshape or it may be formed in two or more shapes. Possible shapes thatthe nanoparticles can assume include spherical shapes, rod shapes,elliptical shapes or any irregular shapes. In the case of rod shapednanoparticles, they may have a diameter of between about 10 nm to 50 nm,a length of 50 to 400 nm, and an aspect ratio of more than 5, but notlimited thereto.

In order to provide efficient interaction between the reactivenanoparticles and the water vapour/oxygen permeating the barrier layer,the nanoparticles occupying the defects may have suitable shapes thatwould maximise the surface area that can come into contact with thewater vapour and oxygen. This means that the nanoparticles may bedesigned to have a large surface area to volume, or surface area toweight ratio. In one embodiment, the nanoparticles have a surface areato weight ratio of between about 1 m²/g to about 200 m²/g. Thisrequirement can be achieved by using nanoparticles with differentshapes, such as 2, 3 or more different shapes as described above.

A binder in which the nanoparticles are distributed may be used in thesealing layer. Materials suitable for use as the binder includepolymers, such as polymers derivable from monomers having at least onepolymerisable group, and which can be readily polymerised. Examples ofpolymeric materials suitable for this purpose include polyacrylate,polyacrylamide, polyepoxide, parylene, polysiloxanes and polyurethane orany other polymer. For strong adhesion between 2 successive barrierlayers, or to adhere the multilayer film onto a substrate, the polymerswith good adhesive quality may be chosen. The sealing layer containingthe nanoparticles is typically formed by coating the barrier with adispersion containing nanoparticles mixed with a monomer solution, e.g.an unsaturated organic compound having at least one polymerisable group.Thickness of the sealing layer comprising binder with distributednanoparticles therein can be in the range of about 2 nm to about severalmicrometers.

In some embodiments, the sealing layer is arranged to be in closeproximate contact with the entire surface of the barrier layer. Forexample, the sealing layer may be formed over the barrier layer in sucha manner that it conforms to the shape of defects present on the surfaceof the barrier layer, i.e. either occupying or filling up entirely thepits present in the at least one barrier layer, or levelling roughprotrusions over the surface of the barrier layer. In this manner,defects giving rise to the permeation of corrosive gases through theencapsulation barrier stack are “plugged”, while protrusions which wouldotherwise give rise to poor interfacial contact between barrier layersare levelled. Any conformal coating or deposition method can be used,e.g. chemical vapour deposition or spin coating. Atomic layer depositionand pulsed laser deposition may also be used to form the sealing layer.

The barrier material used for forming the barrier layer of themultilayer film may comprise any typical barrier material with lowpermeability to water vapour and/or oxygen in the bulk phase. Forexample, the barrier material may comprise metals, metal oxides,ceramics, inorganic polymers, organic polymers and combinations thereof.In one embodiment, the barrier material is selected from indium tinoxide (ITO), TiAlN, SiO₂, SiC, Si₃N₄, TiO₂, HfO₂, Y₂O₃, Ta₂O₄, andAl₂O₃. The thickness of a barrier layer may be between 20 nm to 80 nm.In this respect, materials for reactive nanoparticles can be used as thebarrier layer since the reactivity of the material depends on its size.For example, although nanoparticulate Al₂O₃ is reactive towards water, abulk layer of Al₂O₃ which has larger than nanoscale dimensions does notdisplay the same level of reactivity with water, and can thus be usedfor the barrier layer.

For certain applications which require the encapsulation barrier stackto have good mechanical strength, a substrate may be provided to supportthe multilayer film. The substrate may be flexible or rigid. Thesubstrate may comprise any suitable variety of materials such aspolyacetate, polypropylene, polyimide, cellophane,poly(1-trimethylsilyl-1-propyne, poly(4-methyl-2-pentyne), polyimide,polycarbonate, polyethylene, polyethersulfone, epoxy resins,polyethylene terepthalate, polystyrene, polyurethane, polyacrylate,polyacrylamide, polydimethylphenylene oxide, styrene-divinylbenzenecopolymers, polyvinylidene fluoride (PVDF), nylon, nitrocellulose,cellulose, glass, indium tin oxide, nano-clays, silicones,polydimethylsiloxanes, biscyclopentadienyl iron, or polyphosphazenes, toname some illustrative examples. The base substrate may arranged to facethe external environment and or it may face the encapsulatedenvironment. In food packaging, the substrate may face the internalsurface that is in contact with food while the encapsulation barrierstack forms the external surface in contact with atmospheric conditions.

Although it may be possible to form the multilayer film directly onto asubstrate, a substrate with a rough surface may be undesirable fordirect contact with the barrier layer of the multilayer film. Aninterface layer between the multilayer film and the substrate may beprovided to improve the contact between them. In one embodiment, aplanarising layer is interposed between the substrate and the multilayerfilm so that the interface between the substrate and the multilayer filmis improved. The planarising layer may comprise any suitable type ofpolymeric adhesive material such as epoxy. In a preferred embodiment,the planarising layer comprises polyacrylate (acrylic polymer), aspolyacrylate is known for having strong water absorption properties. Inthe absence of a planarising layer, the multilayer film may beorientated such that the sealing layer is in contact with the surface ofthe substrate, for example.

The barrier effect of a single barrier layer coupled with a sealinglayer, i.e. a single ‘paired layer’, is additive, meaning that thenumber of pairs of barrier/sealing layers coupled together isproportional to the overall barrier property of the multilayer film.Accordingly, for applications requiring high barrier properties, aplurality of paired layers may be used. In one embodiment, each barrierlayer is stacked on top of each sealing layer in alternating sequence.In other words, each sealing layer acts as an interface layer between 2barrier layers. In some embodiments, 1, 2, 3, 4, or 5 paired layers arepresent in the multilayer film. For general purpose applications inwhich water vapour and oxygen permeation rates are less stringent (e.g.less than 10⁻³ g/m²/day), the multilayer film may include only 1 or 2barrier layers (1, 2 or 3 sealing layers would correspondingly bepresent), whereas for more stringent applications, 3, 4, 5 or morebarrier layers may be included in the multilayer film to achieve watervapour permeation rates of less than 10⁻⁵ g/m²/day or preferably lessthan 10⁻⁶ g/m²/day. Where more than 2 paired layers are used, eachpaired layer may be formed on opposing sides of the substrate to providea double-laminated substrate, or they be formed on the same side of thesubstrate.

In order to protect the multilayer film from mechanical damage, themultilayer film may be capped or overlaid with a terminal protectivelayer. The terminal layer may comprise any material having goodmechanical strength and is scratch resistant. In one embodiment, theterminal layer comprises an acrylic film having distributed therein LIEand/or MgF₂ particles.

The encapsulation barrier stack according to the invention may be usedfor any suitable barrier application, such as in the construction of acasing or housing, or a barrier foil for blister packs, or it may beused as an encapsulating layer over an electronic component. Theencapsulation barrier stack may also be laminated over any existingbarrier material, such as packaging materials for food and drinks, toimprove their existing barrier properties. In a preferred embodiment,the encapsulation barrier stack is used to form an encapsulation forprotecting electroluminescent electronic components comprising moistureand/or oxygen sensitive reactive layers, wherein the electroluminescentcomponent is encapsulated within the encapsulation. Examples of suchdevices include, but are not limited to, reactive components comprisedin Organic Light Emitting Devices (OLEDs), charged-coupled devices(CODs), and micro-electro-mechanical sensors (MEMS).

In OLED applications, the encapsulation barrier stack may be used toform any part of an encapsulation for isolating the active component ofthe OLED device. In one embodiment, the encapsulation barrier stack isused to form a base substrate for supporting the reactive layers of theelectroluminescent component. In a rim-sealing structure, theencapsulation barrier stack may be used to form a rigid cover that isarranged over the reactive layers of the electroluminescent component.The rigid cover may be attached to the base substrate by means of anadhesive layer, the adhesive layer being arranged at least substantiallyalong the edge of the cover substrate for forming an enclosure aroundthe reactive component. In order to minimise lateral diffusion ofoxygen/moisture into the enclosure containing the reactive component,the width of the covering layer or the adhesive layer may be made largerthan the thickness of the encapsulation barrier stack.

In another embodiment, the encapsulation barrier stack is used to form aflexible encapsulating layer which seals the electroluminescentcomponent against the base substrate. In this case, such anencapsulating layer may wrap around the surface of theelectroluminescent component to form a ‘proximal encapsulation’. Theshape of the encapsulating layer thus conforms to the shape of thereactive component, leaving no gap between the electroluminescentcomponent to be encapsulated and the encapsulating layer.

The present invention is further directed to a method of forming anencapsulation barrier stack according to the invention. The methodcomprises forming at least one barrier layer and at least one sealinglayer. As the sealing layer contains reactive nanoparticles, stepsinvolving the preparation and the use of the sealing layer is preferablycarried out under vacuum to preserve the reactivity of the nanoparticlestowards the moisture and/or oxygen. The step of forming the sealinglayer comprises mixing a polymerisable compound with a nanoparticledispersion to form a sealing mixture, and polymerising the sealingmixture under vacuum to form a sealing layer. The nanoparticledispersion may comprise nanoparticles dispersed in at least one organicsolvent. The at least one organic solvent may include any suitablesolvent, such as ethers, ketones, aldehydes and glycols for example.

Nanoparticles may be synthesised by any conventional method known in theart, including vapor phase synthesis (Swihart, Current Opinion inColloid and Interface Science 8 (2003) 127-133), sol-gel processing,sonochemical processing, cavitation processing, microemulsionprocessing, and high-energy ball milling, for instance. Nanoparticlesare also commercially available either as nanoparticle powders or in aready-made dispersion from Nanophase Technologies Corporation, forexample. Proprietary methods may be used to synthesise commerciallyobtained nanoparticles such as NanoArc® synthesis.

In one embodiment, surface-activation of the nanoparticles is carriedout in order to remove contaminants from the surface of thenanoparticles that may interfere with their ability to react withmoisture and/or oxygen. Surface activation may comprise treating thenanoparticles with an acid, including mineral acids such as hydrochloricacid or sulphuric acid. The acid used for said treatment is preferably adilute acid. Treatment comprises immersing the nanoparticles in the acidfor a period of about 1 hour. It is to be noted that nanoparticles whichcan be easily contaminated such as carbon nanotubes and carbonnanofibres may require surface activation. On the other hand,nanoparticles such as aluminium oxide and titanium oxide may not requiresurface activation since these nanoparticles have high surface energy.

The polymerisable compound may be any readily polymerisable monomer.Suitable monomers are preferably readily polymerisable via UV curing orheat curing or any other convenient curing method.

In one embodiment, polyacrylamide is used as polymer for binding thenanoparticles. Acrylic acid monomer powder may be dissolved in polarorganic solvents such as 2-methoxyethanol (2MOE) and ethylene glycol(EG). In order to obtain a uniform distribution of the nanoparticles inthe sealing mixture, sonification of the sealing mixture mayadditionally be carried out. For instance, sonification may be carriedout for at least about 30 minutes prior to polymerisation.

A substrate may be a part of the device to be encapsulated, such as apart of a circuit board, or it may be an additional structure that isincluded as part of the encapsulation, such as a flexible substrate. Itis also possible that the substrate is part of the encapsulation barrierstack, comprising a thick barrier layer on which further sealing layersand barrier layers are subsequently deposited. Otherwise, the substratemay be the surface of a worktop for fabricating the multilayer film andas such does not form part of the encapsulation barrier stack.

Once the substrate has been provided, it can be coated with barrierlayers and the sealing solution. The barrier layer can be formed viaphysical vapor deposition (e.g. magnetron sputtering, thermalevaporation or electron beam evaporation), plasma polymerization, CVD,printing, spinning or any conventional coating processes including tipor dip coating processes.

The sealing solution may be formed on the barrier layer via any solgelmethod such as spin coating, screen printing, WebFlight method, tipcoating, CVD methods or any other conventional coating methods. Metaloxide and metal nano-particles, as well as carbon nanotubes, can beco-evaporated along with monomer or dimers of parylene based polymerfilms. Any type of parylene dimers including parylene C or D or anyother grades can be evaporated along with nano particles.

If multiple barrier/sealing layers, i.e. paired layers, are to beformed, a substrate can be repetitively coated with the barrier materialand sealing solution in. In order to establish an alternatingarrangement comprising successive barrier layer and sealing layer, thesubstrate may be successively coated first with the barrier material andthen the sealing solution repeating over several times until theintended number of layers are formed. Each time the sealing solution isapplied, it is preferably UV cured prior to the formation of the nextbarrier layer over it.

After the sealing and barrier layers have been formed, optional stepsmay be taken to complete the construction of the encapsulation barrierstack, such as the formation of a glass cover, ITO lines and ITOcoating. For example, Passive Matrix displays may require ITO lines tobe formed on the encapsulation barrier stack. After the cover has beenformed, the exposed surface of the cover may be further protected with aprotective coating via deposition of a capping layer (MgF/LiF coating).

These aspects of the invention will be more fully understood in view ofthe following description, drawings and non-limiting examples.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments will now be described by way of non-limitingexamples only, with reference to the accompanying drawings, in which:

FIG. 1A depicts an encapsulation barrier stack according to oneembodiment of the invention. FIG. 1B depicts a conventional barrierstack. FIGS. 1C and 1D depicts other embodiments of the encapsulationbarrier stack which comprise a base substrate.

FIG. 2A, FIG. 2B and FIG. 2C depict various implementations of theencapsulation barrier stack for encapsulating an OLED device.

FIG. 3 shows a process flow diagram for fabricating an encapsulationbarrier stack.

FIG. 4 and FIG. 5 shows a setup for carrying out an investigation of thebarrier properties of fabricated encapsulation barrier stacks using acalcium sensor.

FIG. 6 shows the optical images of 4 different encapsulation barrierstacks, Stacks A, B, C, and D, after exposure to moisture.

FIG. 7 shows 70× magnification SEM images of 3 encapsulation barrierStacks A to C made according to the invention.

FIG. 8 shows the morphology of the 3 encapsulation barrier Stacks A to Cmade according to the invention.

FIG. 9 shows an embodiment of the encapsulation barrier stack of theinvention comprising a capping acrylic film. The encapsulation barrierstack was used for quantitative analysis.

FIG. 10 shows a graph of Electrical Conductance vs Time for theencapsulation barrier stack shown in FIG. 9.

FIG. 11 shows a graph of Transmittance vs Wavelength for theencapsulation barrier stack shown in FIG. 9.

FIG. 12 shows the scanning electron microscopy (SEM) images of barrierstacks D, E and F.

FIG. 13 shows the graph of transmittance vs. wavelength forencapsulation barrier stacks A, C, D, E and F.

FIG. 14 shows the graph of Conductance vs. Time for encapsulationbarrier stacks D, E and F.

FIG. 15 shows the Load Strain performance curve for barrier stacks D, Gand H.

DETAILED DESCRIPTION

FIG. 1A shows one embodiment of an encapsulation barrier stack 100according to the invention. The encapsulation barrier stack 100comprises a multilayer film 102 comprising barrier layers 103 andsealing layers 105. The barrier layers 103 have low permeability tooxygen and/or moisture. It will be noted that barrier layers 103 containpinhole defects 107 which extend through the thickness of the barrierlayer 103. Pinhole defects along with other types of structural defectslimit the barrier performance of barrier layers as oxygen and watervapour can permeate into the barrier layer via these defects, eventuallytraversing the encapsulation barrier stack and coming into contact withthe oxygen/moisture sensitive device. For illustrative purposes, FIG. 1Adepicts only pinhole defects. In reality, other types of structuraldefects such as pits and cracks may also be present.

The sealing layers 105 comprise reactive nanoparticles capable ofinteracting with water vapour and/or oxygen, thereby retarding thepermeation of oxygen/moisture through the encapsulation barrier stack.In accordance with the present invention, these defects are at leastpartially covered up, or in some embodiments, entirely filled up by thenanoparticles in the sealing layer 105.

FIG. 1B depicts a conventional barrier stack 120 which comprises barrierlayers 123 and planarising adhesive layers 125 are arranged on asubstrate 121. Although inorganic metal oxide barrier layers haverelatively high gas impermeability, pinhole defects present in thebarrier layer allow moisture and oxygen to permeate through the barrierlayer. In the figure, pinhole defects 127 in the barrier layers 123 areexposed to the environment, so moisture and oxygen are able to permeatethrough the barrier layer. For example, oxygen and moisture can permeatethrough the barrier layer 1231 via pinhole defects, and thenprogressively permeate through the adhesive layer 1251, and subsequentlypermeate through barrier layer 1232 and adhesive layer 1252 to reach thesubstrate 121 where an oxygen/moisture sensitive device is typicallylocated.

FIG. 1C depicts yet another embodiment of a barrier stack 140 accordingto the invention wherein the multilayer film 142 comprises one barrierlayer 143 and only one sealing layer 145 arranged over it. The barrierstack 140 further comprises a base substrate 141 for supporting themultilayer film. A planarising layer 144 is interposed between the basesubstrate 141 and the multilayer film 142 included to improve thecontact between the multilayer film and the substrate. A single pairedlayer in accordance with this embodiment can be used for applicationswith less stringent barrier requirements.

The foregoing embodiments show an encapsulation barrier stack in whichthe multilayer film is laminated onto only one side of a substrate. FIG.1D shows a double-laminated substrate in which a multilayer film islaminated to both sides of a base substrate. Encapsulation barrier stack160 comprises a substrate 161 that is sandwiched between two multilayerfilms 1621 and 1622. Multilayer film 1621 comprises 3 barrier layers 163and three nanoparticulate sealing layers 165. Multilayer film 1622comprises 1 barrier layer and 2 sealing layers. Each respective layer isarranged in alternating sequence such that the sealing layers form theinterlayer between any 2 barrier layers. In this embodiment, sealinglayers 165 are in direct contact with the substrate 161, thereby servingas planarising layers. By forming 5 paired layers on the substrate, thisembodiment provides an encapsulation barrier stack with high gas barrierproperties.

The encapsulation barrier stack of the invention can be used in severalways for encapsulating a moisture and oxygen sensitive device such as anOLED. For example, it can be laminated onto a conventional polymersubstrate that is used to support the OLED. FIG. 2A shows anencapsulated OLED comprising electrodes 214 and reactive layer 216within a rim-sealed encapsulation. In this embodiment, the encapsulationbarrier stack comprises a base substrate 201 and a multilayer film 212.The base substrate 201 is laminated with the multilayer film 212comprising barrier layer 203 and two sealing layers 205 sandwiching thebarrier layer 203. Pinhole defects 207 in the barrier layer 203 aresealed by the nanoparticulate material of the sealing layer. The OLED isarranged directly on the multilayer film 212, and encapsulated under aglass cover 210. Rim adhesive 209 serves to adhere the glass cover 210to the encapsulation barrier stack, thereby forming an encapsulationaround the OLED.

FIG. 2B shows another embodiment in which the encapsulation barrierstack of the invention is used as a cover substrate. The substrate 201is not laminated by the encapsulation barrier stack (although it may belaminated if desired). In place of the glass cover is the encapsulationbarrier stack comprising rigid multilayer film 222 (without asubstrate). The multilayer film similarly comprises barrier layer 203sandwiched between sealing layers 205, and its defects 207 are filledwith the nanoparticulate material. The OLED is encapsulated underneaththe multilayer film, meaning that in order for the light emitted by theOLED to be clearly seen, the multilayer film 222 should be sufficientlytransparent. The multilayer film 222 is attached to the base substrateby means of rim adhesive 209. when implementing rim sealing as shown inFIG. 2A or FIG. 2B, the width of the rim adhesive is typically in themillimeter or centimeter scale, which is substantially larger than thethickness of the base substrate or the encapsulation barrier stack.Accordingly, lateral diffusion of water vapour and oxygen through therim adhesive would in such a case be substantially longer thantransverse diffusion through the encapsulated barrier stack.

Other than rim sealing as depicted in FIG. 2A and FIG. 2B. In thefollowing figure, thin-film encapsulation comprising the attachment ofan encapsulation barrier stack over the OLED, hereinafter referred to as‘proximal encapsulation’, is also possible. Proximal encapsulation is inparticular suitable for flexible OLED devices. FIG. 2C shows anembodiment in which an OLED comprising electrodes 214 and reactive layer216 is encapsulated between a flexible base substrate 201 and a flexibleencapsulation barrier stack arranged proximally over the OLED comprisingmultilayer film 232. It will be noted that the multilayer film 232conforms to the external shape of the OLED device.

Although FIGS. 2A, 2B and 2C depict the encapsulation of an OLED, theencapsulation barrier stack of the present invention is by no meanslimited to such an application. It will be understood by the skilledperson the any article can be encapsulated in place of an OLED,including pharmaceutical drugs, jewelry, reactive metals, electroniccomponents, and food substances, for example.

The general scheme of fabrication of the encapsulation barrier stackaccording to the invention is shown in FIG. 3. A polycarbonate or PETsubstrate is provided for forming the encapsulation barrier stack. Thesubstrate is plasma treated and coated with alumina barrier material viamagnetron sputtering, thereby forming a barrier layer. Concurrently, asealing solution comprising alumina and TiO₂ nanoparticles is mixed withan acrylic acid monomer solution, thereby forming a sealing solution.The sealing solution is web flight coated onto the barrier layer, forexample, via a roll-to-roll process. The coating of barrier layer andsealing layer is repeated for a predetermined number of times to obtaina multilayer film with a desired barrier property. For example, amultilayer film comprising 5 paired layers will require the magnetronsputtering and web flight coating to be repeated 5 times to form 5paired layer. It is to be noted that it is also possible, in otherembodiments, to form an initial coat of sealing layer over thesubstrate. The sealing layer acts as a planarising material whichsmoothens the surface of the substrate thereby covering defects on thesubstrate which could provide pathways for the infiltration ofmoisture/oxygen.

After the multilayer film is formed, ITO is magnetron sputtered over themultilayer film to form an ITO coating. If the encapsulation barrierstack is to be used in Passive Matrix displays, only ITO lines arerequired instead of a complete coat of IOT. A protective liner issubsequently formed on the ITO coating. Any suitable material may beused, depending on the intended purpose, e.g. scratch resistant films orglare reduction films, such as MgF/LiF films. After forming theprotective film, the encapsulation barrier stack is packed in aluminiumfoil packaging or slit into predetermined dimensions for assembly withother components.

Specific examples will now be described to illustrate the fabricationprocess as described above as well as the barrier performance offabricated encapsulation barrier stacks.

Example 1 Fabrication and Characterisation of Encapsulation BarrierStacks With Sealing Layer Comprising Metal Oxide Nanoparticles

a) Synthesis of Encapsulation Barrier Stacks A, B and C

As an illustrative example, three different encapsulation barrier stackseach comprising different nanoparticles in the sealing layer werefabricated. Each of the encapsulation barrier stacks were made accordingto the following specification:

Stack A

-   -   1. Base substrate—Polycarbonate film (188 μm thick)    -   2. Planarizing layer—Plain acrylic polymer    -   3. First Barrier layer—ITO (indium tin oxide)    -   4. Sealing layer—aluminium oxide nanoparticle    -   5. Second barrier layer—ITO        Stack B    -   1. Base substrate—Polycarbonate film (188 μm thick)    -   2. Planarizing layer—Plain acrylic polymer    -   3. First Barrier layer—ITO    -   4. Sealing layer—titanium oxide nanoparticle    -   5. Second barrier layer—ITO        Stack C    -   1. Base polymer Substrate—Polycarbonate film (188 μm thick)    -   2. Planarizing layer—Plain acrylic polymer    -   3. First Barrier layer—ITO    -   4. Sealing layer—Aluminium oxide and Titanium oxide nanoparticle    -   5. Second barrier layer—ITO

For comparison, a conventional barrier stack, Stack D, comprising aconventional multi-layer stack structure, was fabricated. Stack Dcomprised the following stack structure:

Stack D

-   -   1. Base substrate—Polycarbonate film (188 μm thick)    -   2. Planarising layer—Plain acrylic polymer    -   3. First Barrier layer—ITO    -   4. Second Planarising layer—Plain acrylic polymer    -   5. Second Barrier layer—ITO        Step (i): Surface Preparation of Substrate

Polycarbonate substrates are transparent and can be cut into preferreddimensions. Pneumatically operated hollow die punch-cutting equipment orany conventional slitting machine can be used to slit the polycarbonatesubstrates into the specified or required dimensions.

The substrates are rinsed with isopropyl alcohol (IPA) and blow-driedwith nitrogen to remove macro-scale adsorbed particles on the surface.After nitrogen blow-dry, the substrates are placed in the vacuum oven ata pressure of 10⁻¹ mbar for degassing absorbed moisture or oxygen.

Immediately after the degassing process, the substrates are transferredto the plasma treatment chamber (e.g. ULVAC SOLCIET Cluster Tool). RFargon plasma is used to bombard the surface of the barrier film with lowenergy ions in order to remove surface contaminants. The base pressurein the chamber was maintained below 4×10⁻⁶ mbar. The argon flow rate is70 sccm. The RF power is set at 200 W and an optimal treatment timeusually 5 to 8 eight minutes is used depending on the surface condition.

After cleaning of the base substrate was carried out, plain acrylicpolymer was spin coated onto the polycarbonate substrates to form aninterface planarising layer.

Step (ii): Metal Oxide Barrier Layer Coating

Indium tin oxide barrier layers were prepared by unbalanced magnetronsputtering techniques as follows. Sputtering was used to deposit themetal oxide barrier layer onto the planarising layer. Unbalancedmagnetron sputtering technique was used to form high density oxidebarrier films. In this sputtering technique, a metal layer of typicallya few mono-layers will be deposited from an unbalanced magnetron, andthen oxygen will be introduced to the system to create oxygen plasma,directed towards the substrate to provide argon and oxygen ionbombardment for a high packing-density oxide film. Plasma helps toincrease the reactivity of the oxygen directed onto the growing filmsurface and provides for more desirable rheology. In order to depositdense films without introducing excessive intrinsic stresses, a highflux (greater than 2 mA/cm²) of low energy (˜25 eV) oxygen and argonions to bombard the growing barrier oxide films.

The continuous feedback control unit is used to control the reactivesputtering processes. The light emitted by the sputtering metal in theintense plasma of the magnetron racetrack is one indicator of the metalsputtering rate and the oxygen partial pressure. This indication can beused to control the process and hence achieve an accurate oxide filmstoichiometry. By using a continuous feedback control unit from a plasmaemission monitor, reproducible films and desirable barrier propertieswere obtained.

Step (iii): Sealing Layer Coating

Commercially available nanoparticles (e.g. #44931 NanoDur® 99.5%aluminium oxide particles from Nanophase Technologies) were pre-treatedwith plasma and added to an organic solvent, such as 2-methoxyethanol(2MOE) and ethylene glycol (EG) for dispersion in the ratio of 1:1 2MOEto EG. Propylene glycon monomethyl ether or Ethyl Acetate or MethylIsobutyl Ketone, Methyl Ethyl, 2 MOE or any mixture of solvents orwetting additive agents can be used as well. Alternatively, commerciallyavailable nanoparticle dispersions such as aluminium oxide, zinc oxide,or titanium oxide dispersed in Hexane diol diacrylate, Isobornylacrylate, Tripropylene glycol diacrylate can be used (e.g. a colloidaldispersion of 45 nm APS aluminum oxide dry powder, NanoDur® X1130PMA,50% dispersed in 1,2-Propanediol monomethyl ether acetate from NanophaseTechnologies).

A polymerizable group compound like commercially available UV curableacrylate monomers (Addision Clear Wave—HC-5607) is added to thenanoparticle mixture to form a sealing solution. The polymer coatingweight may be between the amount of 30% to 50%. For example, the totalconcentration of nanoparticles in the polymer may at 66% by weight ofthe sealing solution, while polymer coating weight is at about 34% byweight of the sealing solution.

The synthesis was undertaken under inert gas environment. The set ofexperiments were carried out with different mixture of nanoparticles inacrylic polymer solutions and spin coated onto the plain polymersubstrate (above FIG. 5).

Each of the samples A, B and C were made according to the general steps(i), (ii) and (iii) using different constituents as explained in thefollowing.

For sample encapsulation barrier stack A, 30 ml of UV curable acrylatemonomer with a coating weight of about 50% of the sealing solution wasadded to 15 ml of a dispersion of aluminium oxide in tripropylene glycoldiacrylate (35% weight), obtainable from Nanodur of NanophaseTechnologies. 5 ml of an organic solvent of 2-MOE and EG (1:1) ratio wasadded to the mixture. Sonification of the mixture was then carried outfor about 1 hour prior to deposition onto a barrier oxide layer.

For sample encapsulation barrier stack B, 30 ml of UV curable acrylatemonomer with a coating weight of about 50% of the sealing solution wasadded to 10 ml of titanium (IV) oxide dispersed in isopropanol 40% byweight, obtainable from Nanodur of Nanophase Technologies. 10 ml of anorganic solvent of 2-MOE and EG (1:1) ratio was added to the mixture.Sonification of the mixture was then carried for about 1 hour prior todeposition onto a barrier oxide layer.

For sample encapsulation barrier stack C, 30 ml of UV curable acrylatemonomer with a coating weight of about 50% by weight of the sealingsolution was added to (a) 7.5 ml of dispersed aluminium oxide intripropylene glycol diacrylate (35% weight), obtainable from Nanodur ofNanophase Technologies, and (b) 5 ml of Titanium (IV) oxide dispersed inIsoproanal with 40% weight with 2 MOE and Ethylene glycol (1:1 ratio).Sonification of the mixture was then carried for about 1 hour prior todeposition onto a barrier oxide layer.

The formation of the sealing layer via spin coating was undertaken in anitrogen atmosphere in a glove box. The oxygen and water vapour contentswere reduced to less than 1 ppm level in the glove box.

Characterisation of Encapsulation Barrier Stacks A, B and C

After plasma treatment process, the encapsulation barrier stacks aretransferred to a vacuum evaporation chamber (thermal evaporation) undervacuum. The barrier stacks are then evaluated for their barrierproperties using the calcium sensor described in WO 2005/095924. Bothqualitative evaluation and quantitative evaluation were carried out.

In qualitative evaluation, a test cell as shown in FIG. 4 is formedusing the fabricated encapsulation barrier stacks. Briefly, two metaltracks with dimensions of 2 cm by 2 cm are fabricated. A sensing elementhaving dimensions of 1 cm length, 2 cm width and 150 nm thickness isformed in between the two electrodes. The measured resistivity of thesensing element is 0.37 Ω-cm. After the deposition process, a load locksystem is used to transfer the sample to a glove box under dry nitrogenat atmospheric pressure. After the calcium deposition, a 100 nm silverprotection layer was deposited for the qualitative analysis.

In the case of the quantitative resistance measurement, a test cell asshown in FIG. 5 is formed using the fabricated encapsulation barrierstacks. 300 nm of silver was used for the conductive track, 150 nmcalcium was used as the sensor and 150 nm lithium fluoride was used as aprotection layer. After the deposition processes, a UV curable epoxy wasapplied on the rim of the substrate and then the whole substrate wassealed with a 35 mm×35 mm glass slide. Desiccants were attached to the35 mm×35 mm cover glass slide for absorbing any water vapour present dueto out gassing or permeation through the epoxy sealing. A load locksystem was used for the entire process and the test cells wereencapsulated in the glove box under dry nitrogen at atmosphericpressure. To accelerate the permeation tests, the samples were placedinto a humidity chamber at constant temperature and humidity of 80° C. &90% RH respectively. These were viewed optically at regular intervalsfor a qualitative degradation test and analysis of the defects, andmeasured electrically for the quantitative analysis of the degradation.The calcium test cell's conductive track terminals are connected to aconstant current source (Keithey source meter), which is interfaced witha computer. Resistance of the calcium sensor/silver track is monitoredevery second and plotted automatically by the computer using lab viewsoftware. A Dynamic Signal Analyzer with a FFT analysis is used to takethe noise spectrum measurement automatically at periodic intervals ofone second.

The calcium degradation test provides qualitative visual information ondefects such as pinholes cracks and nano-pores, because the permeatedwater vapors diffuse through the defects of the substrate and itsbarrier layer(s) and react with the calcium sensor to formdistinguishable patches on the calcium sensing element. Micro-pores andsub-micron sized pores such as pinholes and cracks in a transparentcoating are very difficult to discern or to study even by sophisticatedsurface microscopy techniques (e.g. SEM). In the present experiment, thecolour contrast between oxidized and non-oxidized calcium was used forqualitative analysis. The degradation was monitored using opticalmicroscopy. The images were taken at intervals of typically severalhours. From the images the calcium-corroded spots could be directlylinked to defects of the barrier films. Further, growth dynamics of thecalcium corrosion could provide qualitative information of barrierproperties.

The images in FIG. 6 highlight the nature of the defects exhibited on AB, C films that have been tested and the barrier structure is shown inFIG. 6. The degradation images in FIG. 6 show that the barrier stacks Aand C have significantly better barrier properties as compared toconventional barrier stacks as exemplified by barrier stack D. Calciumsensor degradation in barrier stack A commenced at 80 hours and theentire calcium degraded by 270 hours. Calcium sensor degradation inbarrier stack C did no show any significant degradation until after 470hours.

FIG. 7 shows scanning electron microscopy (SEM) images of barrier stacksA, B & C immediately after fabrication. The surfaces of these threebarrier Stacks are smooth and no agglomeration of nanoparticles isobserved. These images confirm that the dispersion of the nanoparticlesin the sealing layer is uniform, so that the barrier stack isconsequently transparent. The further investigation on water vaportransport properties were carried out with permeation measurement systemand discussed with next section.

FIG. 8 shows images of the surface of the sealing layers as studied withSEM and AFM. The surface properties were compared with of that of plainacrylic polymer coatings. The AFM picture shows that the uniformdispersion of nanoparticles in solution A, B and C was achieved. Thesurface roughness measured for barrier stacks A and B films are wellwithin 0.75 nm at 1 μm to 10 μm scans and comparable with plain acrylicpolymer films. However, for barrier stack C, the surface is relativelyrough (6.5 nm). Roughness may be advantageously used to improve theadhesion between the barrier layer and the substrate.

A test encapsulation barrier stack having the structure shown in FIG. 9was fabricated to carry out a quantitative analysis of the encapsulationbarrier stack samples fabricated in accordance with the above. Anencapsulation barrier stack was fabricated with two ITO barrier layerswere fabricated by magnetron sputtering method and one sealing layer(comprising aluminium oxide nanoparticles) was used to seal the ITOdefects. The outermost terminating layer is plain acrylic film which isnormally used for WVTR measurement purpose. In principle, only one ITObarrier layer's defects were sealed. In this embodiment, the sealinglayer comprises Al₂O₃ nanoparticles with sizes of 20 nm to 40 nm.

The plot of calcium conductance against time is shown in FIG. 10 for theencapsulation barrier stack. The corresponding change in calcium (mol)can be derived from the graph. The water vapour transmission rate of theencapsulation barrier stack comprising one barrier layer and one sealinglayer is determined to be 1×10⁻³ g/m²/day at 80° C. & 90% relativehumidity. In contrast, conventional multi-layer stacks with two barriersSiN layer and plain acrylic interlayer showed performance of only about10⁻¹ g/m²/day level at 70° C. & 90% relative humidity condition.

Therefore, these results demonstrate that by sealing off the defects ofone barrier layer with a nanoparticulate sealing layer, the barrierperformance is improved up to two orders in higher magnitude as comparedto the plain acrylic film based multi-layer substrate. If the defects inthree or more barrier layers are sealed using two or more sealing layerscomprising reactive nanoparticles, the water vapour barrier performancecan be less than 10⁻⁵ g/m²/day, or even less than 10⁻⁶ g/m²/day.

The single-layered encapsulation barrier stack comprising polycarbonate(188 μm)/ITO/Nanostructured sealing layer with aluminium and titaniumnanoparticle and the double-layered encapsulation barrier stack withPC/ITO/sealing layer/ITO/sealing layer was fabricated. The opticalproperties measured the spectral transmission in the UV and visibleregion of the spectrum was measured with UV-Vis spectrometer. It showsthat the light transmittance of double stack is 82% and single stack isabout 85%. The reduction of transmission is due to ITO film propertiesand nature.

Example 2 Fabrication and Characterisation of Encapsulation BarrierStacks with Sealing Layer Comprising Carbon Nanotubes

The following encapsulation barrier stacks with differing carbonnanotube compositions in the sealing layers were prepared:

Stack E

-   -   1. Polycarbonate (188 μm) as base substrate    -   2. ITO as barrier layer    -   3. Nanostructured sealing layer with MCNTs at 0.006%        concentration as sealing layer        Stack F    -   1. Polycarbonate (188 μm) as base substrate    -   2. ITO as barrier layer    -   3. Nanostructured sealing layer with MCNTs at 0.05%        concentration as sealing layer

Pre-treated 10 nm diameter multiwalled nanotubes (hereinafter ‘MCNT’)were first added to a solution mixture of 2-methoxyethanol (2MOE) andethylene glycol (EG) for dispersion. The ratio of 2MOE to EG is 1:1. Thenanotubes were dispersed uniformly into the acrylic polymer viasonification. The synthesis was undertaken under inert gas environment.

Stack E comprises MCNT in the amount of 0.006% by weight, and solution Fcomprises MCNT in the amount of 0.05% by weight. The sealing layers were2 μm thick. The synthesis and fabrication of thin films of sealinglayers were under taken in the glove box which has partial pressure ofnitrogen. The oxygen and water vapour contents were controlled with lessthan 1 ppm level in the glove box.

Stack D as fabricated in Example 1 was used for the comparison of thecharacteristics of the barrier stacks E and F.

The stacks comprising MCNT in the sealing layer were compared with StackD. FIG. 12 shows scanning electron microscopy (SEM) images of Stacks D,E & F films. The surfaces of E and F sealing films are smooth and noagglomeration of MCNT is noticed. These results show that the dispersionof MCNT in the sealing layer is uniform and that the films aretransparent. Further investigation on water vapour transport propertiesand optical properties were carried out with permeation measurementsystem and spectrometer and discussed below.

The optical properties of each barrier stack were measured with spectraltransmission in the UV and visible region of the spectrum with UV-VisSpectrometry.

As can be seen from FIG. 13, conventional acrylic film coated substrate(D) has very high transmission with 99%. However, it does not block UVlight. It shows that the light transmittance of double stack is 82% andsingle stacks are about 85%. The CNT contained encapsulation barrierstack E & F shows transparency about 85%. The reduction of double stacktransmission is due to ITO film properties and nature. The figure alsoshows that the nanoparticle dispersion of the films A, C, E & F areuniform, have no agglomeration and therefore, the light transmission isin the range of 82 to 89%.

The quantitative calcium degradation results of FIG. 14 show that thebarrier stack E and barrier stack F shows significantly better overallbarrier properties than conventional barrier stack D. The initialcalcium sensor degradation/water vapour desorption rates similar for allencapsulation barrier stacks E, F and D at 15 hours and the measuredWVTR is 0.03 g/m²/day level. However, after reaching 20 hours, thesteady state water vapour transmission rates of D is 0.1 g/m²/day andthe entire calcium was degraded before 30 hours. The CNT-containingencapsulation barrier stacks E and F shows the rates of 0.01 g/m²/dayand 0.009 g/m²/day level respectively. After reaching 100 hrs, thebarrier stacks E and F shows a significant improvement in barrierproperties and the WVTR rates was 0.003 g/m²/day.

Without wishing to be bound by theory, it is thought that in barrierstacks E and F, water vapour is drawn into open-ended nanotubes bycapillary suction after 30 hrs of exposure. It is postulated that thetime taken for the water molecule to diffuse into the carbon nanotubesis longer as compared to normal modes of diffusion and therefore, theinitial water vapour desorption was very high. The initialdesorption/permeability results of this invention demonstrated that theprobability of sealing the defects of the barrier layer by CNTs isrelatively low. This may be due to the concentration (0.05%) of CNT usedin the interlayer as compared to the nanoparticles concentration (30% to60%).

To quantify the adhesion properties of an encapsulation barrier stackaccording to the invention, standard peel tests were performed using anInstron test system. The following encapsulation barrier stacks weretested upon:

Stack G

-   -   1. Polycarbonate as base substrate    -   2. ITO as barrier layer    -   3. sealing layer comprising aluminium oxide particles (Al₂O₃        (20% by weight) dispersed in acrylic film        Stack H    -   1. Polycarbonate as base substrate    -   4. ITO as barrier layer    -   5. sealing layer comprising aluminium oxide particles (Al₂O₃        (15% by weight) dispersed acrylic film

Conventional barrier stack D as fabricated in Example 1 was again usedfor comparison. The 2 μm thick sealing layers were deposited onto ITOcoated polycarbonate test substrates and these substrates. They were cutinto the pieces of 10 cm length and 1 cm width and the UV curable epoxy(Three Bond) were applied to a 3 cm long and 1 cm wide area at one endof the sample similar to the ASTM requirements. Surface preparationinvolves the argon plasma cleaning of the above substrates before theapplication of epoxy.

The Load/Strain curve for sample barrier stacks D, G and H were plottedand the results of the test can be seen in FIG. 15. The barrier stacks Dwith the plain conventional acrylic film on ITO surface, the initialinterfacial failure occurred at the interface between the acrylic filmand ITO at 18 N/m and levelling off to steady-state peel strength ofabout 12 N/m. Therefore the adhesion strength of conventional acrylicpolymer onto barrier oxide layer is only 18 N/m. When the barrier stacksG and H were tested, the initial interfacial failure occurred at theinterface between the nanostructured organic sealing layer and ITO at 45N/m for barrier stacks H and 48 N/m for barrier stacks G and levellingoff to steady-state peel strength of about 14-15 N/m for barrier stacksH and G. Therefore the adhesion strength of nanostructured sealingbarrier stacks (G & H) onto barrier oxide layer is 12-15 N/m. Thisresult demonstrates clearly that the adhesion between barrier oxidelayer and nanostructured sealing layer is significantly improved due tothe sealing of the barrier layer's pinholes and defects.

Although this invention has been described in terms of illustrativeembodiments, it has to be understood that numerous variations andmodifications may be made, without departing from the spirit and scopeof this invention as set out in the following claims.

What is claimed is:
 1. An encapsulation barrier stack for encapsulatingat least one of a moisture and oxygen sensitive article, comprising: amultilayer film to be arranged on a substrate, the multilayer filmhaving at least one barrier layer having at least one of low moistureand low oxygen permeability, and at least one sealing layer arranged tobe in contact with a surface of the at least one barrier layer, forplugging at least one defect present in the barrier layer, wherein theat least one sealing layer comprises reactive nanoparticles interactingby way of chemical reaction with at least one of moisture and oxygen toretard the permeation of the at least one of moisture and oxygen throughthe at least one defect present in the barrier layer, wherein thenanoparticles present in the at least one sealing layer plug the atleast one defect present in the at least one barrier layer, wherein thenanoparticles have different at least one of shapes and sizes forcontrolling the sealing and plugging of the at least one defect, whereinthe barrier layer comprises a material selected from indium tin oxide(ITO), TiAlN, SiO₂, SiC, Si₃N₄, TiO₂, HfO₂, Y₂O₃, Ta₂O₅, and Al₂O₃ andwherein a permeation rate of the barrier stack having the at least onesealing layer on the surface of the at least one barrier layer is 10⁻³g/m²/day or less.
 2. The barrier stack of claim 1, wherein thenanoparticles comprise a material selected from the group consisting ofmetals and metal oxides.
 3. The barrier stack of claim 2, wherein thenanoparticles comprise a metal selected from the group consisting of Al,Ti, Mg, Ba and Ca.
 4. The barrier stack of claim 2, wherein thenanoparticles comprise a metal oxide selected from the group consistingof TiO₂, Al₂O₃, ZrO₂, ZnO, BaO, SrO, CaO and MgO, VO₂, CrO₂, MoO₂, andLiMn₂O₄ or a transparent conductive oxide selected from the groupconsisting of cadmium stannate (Cd₂SnO₄), cadmium indate (CdIn₂O₄), zincstannate (Zn₂SnO₄ and ZnSnO₃), and zinc indium oxide (Zn₂In₂O₅).
 5. Thebarrier stack of claim 1, wherein the nanoparticles further comprisecarbon nanotubes.
 6. The barrier stack of claim 5, wherein the amount ofcarbon nanotubes present is about 0.01% to about 10% of the total weightof nanoparticles present in the sealing layer.
 7. The barrier stack ofclaim 1, wherein the sealing layer comprises carbon nanotubes and metaloxide nanoparticles, the quantity of metal oxide nanoparticles presentbeing between 500 to 15000 times (by weight) the quantity of carbonnanotubes present.
 8. The barrier stack of claim 1, further comprisinginert nanoparticles obstructing the permeation of the at least one ofmoisture and oxygen through the at least one defect present in thebarrier layer.
 9. The barrier stack of claim 8, wherein the inertnanoparticles comprise a material selected from the group consisting ofgold, copper, silver, platinum, silica, wollastonite, mullite,monmorillonite, silicate glass, fluorosilicate glass, fluoroborosilicateglass, aluminosilicate glass, calcium silicate glass, calcium aluminumsilicate glass, calcium aluminum fluorosilicate glass, titanium carbide,zirconium carbide, zirconium nitride, silicon carbide, or siliconnitride, metal sulfides, and a mixture or combination thereof.
 10. Thebarrier stack of claim 1, wherein the size of the nanoparticles issmaller than the average diameter of defects present in the at least onebarrier layer.
 11. The barrier stack of claim 1, wherein when the atleast one of the oxygen and moisture sensitive article comprises anelectroluminescent electronic component, the average size of thenanoparticles is less than one-half the characteristic wavelength oflight produced by the electroluminescent electronic component.
 12. Thebarrier stack of claim 1, wherein the sealing layer further comprises apolymeric binder.
 13. The barrier stack of claim 1, further comprising asubstrate for supporting the multilayer film.
 14. The barrier stack ofclaim 13, wherein the multilayer film is orientated such that thesealing layer is arranged on the substrate.
 15. The barrier stack ofclaim 13, wherein the substrate comprises a material selected frompolyacetate, polypropylene, polyimide, cellophane,poly(l-trimethylsilyl-1-propyne, poly(4-methyl-2-pentyne), polyimide,polycarbonate, polyethylene, polyethersulfone, epoxy resins,polyethylene terepthalate, polystyrene, polyurethane, polyacrylate, andpolydimethylphenylene oxide, styrene-divinylbenzene copolymers,polyvinylidene fluoride (PVDF), nylon, nitrocellulose, cellulose, glass,indium tin oxide, nano-clays, silicones, polydimethylsiloxanes,biscyclopentadienyl iron, and polyphosphazenes.
 16. The barrier stack ofclaim 13, further comprising a planarising layer interposed between thesubstrate and the multilayer film.
 17. The barrier stack of claim 1,wherein the multilayer film is arranged on one surface of the substrateor wherein each multilayer film is arranged on each opposing surface ofthe substrate.
 18. The barrier stack of claim 1, further comprising aterminal layer for protecting the multilayer film.
 19. The barrier stackof claim 18, wherein the terminal layer comprises an acrylic film. 20.The barrier stack of claim 19, wherein the acrylic film comprisesdistributed therein at least one of LiF and MgF₂ particles.
 21. Theencapsulation barrier stack of claim 1, wherein the chemical reaction isat least one of hydrolysis or oxidation.
 22. An electronic devicecomprising: an active component that is sensitive to at least one ofmoisture and oxygen, the active component being arranged within anencapsulation barrier stack for encapsulating at least one of a moistureand oxygen sensitive article, the encapsulation barrier stackcomprising: a multilayer film to be arranged on a substrate, themultilayer film having at least one barrier layer having at least one oflow moisture and low oxygen permeability, and at least one sealing layerarranged to be in contact with a surface of the at least one barrierlayer, for plugging at least one defect present in the barrier layer,wherein the at least one sealing layer comprises reactive nanoparticlesinteracting by way of a chemical reaction with at least one of moistureand oxygen to retard the permeation of the at least one of moisture andoxygen through the at least one defect present in the barrier layer,wherein the nanoparticles present in the at least one sealing layer plugthe at least one defect present in the at least one barrier layer,wherein the nanoparticles have different at least one of shapes andsizes for controlling the sealing and plugging of the at least onedefect, wherein the barrier layer comprises a material selected fromindium tin oxide (ITO), TiAlN, SiO₂, SiC, Si₃N₄, TiO₂, HfO₂, Y₂O₃,Ta₂O₅, and Al₂O₃ and wherein a permeation rate of the barrier stackhaving the at least one sealing layer on the surface of the at least onebarrier layer is 10⁻³ g/m²/day or less.
 23. The electronic device ofclaim 22, wherein the encapsulation barrier stack forms a base substratefor supporting the reactive component.
 24. The electronic device ofclaim 22, wherein the encapsulation barrier stack further comprises acovering layer arranged proximally over the active component to form aproximal encapsulation, the reactive component being sandwiched betweenthe covering layer and the encapsulation barrier stack.
 25. Theelectronic device of claim 24, wherein the shape of the covering layerconforms to the external shape of the reactive component.
 26. Theelectronic device of claim 22, wherein the encapsulation furthercomprises a cover substrate attached to the base substrate by means ofan adhesive layer, the adhesive layer being arranged at leastsubstantially along the edge of the cover substrate for forming arim-sealed enclosure around the reactive component.
 27. The electronicdevice of claim 22, wherein the active component is arranged on a basesubstrate, and the encapsulation barrier stack forms an encapsulationlayer over the reactive component that seals the reactive componentagainst the base substrate.
 28. The electronic device of claim 22,wherein the reactive component is selected from the group consisting ofan Organic Light Emitting Device (OLED), charged-coupled device (CCD),and micro-electro-mechanical sensors (MEMS).
 29. A method to manufacturean encapsulation barrier stack, comprising: forming at least one barrierlayer; and forming at least one sealing layer on a surface of the atleast one barrier layer, wherein forming the at least one sealing layercomprises conformal deposition of the at least one sealing layer overthe at least one barrier layer under vacuum or in an inert gasenvironment, wherein the encapsulation barrier stack is forencapsulating at least one of a moisture and oxygen sensitive article,the at least one barrier layer having at least one of low moisture andlow oxygen permeability, wherein the at least one sealing layer isarranged to be in contact with the surface of the at least one barrierlayer to plug at least one defect present in the barrier layer, whereinthe at least one sealing layer comprises reactive nanoparticlesinteracting by way of a chemical reaction with at least one of moistureand oxygen to retard the permeation of the at least one of moisture andoxygen through the at least one defect present in the barrier layer,wherein the nanoparticles present in the at least one sealing layer plugthe at least one defect present in the at least one barrier layer andwherein the nanoparticles have different at least one of shapes andsizes for controlling the sealing and plugging of the at least onedefect, wherein the barrier layer comprises a material selected fromindium tin oxide (ITO), TiAlN, SiO₂, SiC, Si₃N₄, TiO₂, HfO₂, Y₂O₃, Ta₂O₅and Al₂O₃ and wherein a permeation rate of the barrier stack having theat least one sealing layer on the surface of the at least one barrierlayer is 10⁻³ g/m²/day or less.
 30. The method of claim 29, furthercomprising providing a substrate for supporting the barrier stack,wherein the at least one sealing layer is first formed on the substrate.31. The method of claim 30, wherein the substrate comprises at least oneof a barrier layer and a polymer substrate.
 32. The method of claim 29,wherein the conformal deposition comprises mixing a polymeric bindingmaterial with a nanoparticle dispersion comprising nanoparticlesdispersed in a solvent for doping the nanoparticle dispersion with thepolymeric binding material, to form a sealing mixture, and optionallypolymerising the sealing mixture over the at least one barrier layer.33. The method of claim 29, wherein the nanoparticles are distributed ina sealing solution with a concentration of the nanoparticles of at least50% by weight of the sealing solution.
 34. The method of claim 29,wherein the concentration of the nanoparticles is at least 50% and lessthan 70% by weight of the sealing solution.
 35. An encapsulation barrierstack for encapsulating at least one of a moisture and oxygen sensitivearticle, comprising: a multilayer film to be arranged on a substrate,the multilayer film comprising at least one barrier layer having atleast one of low moisture and low oxygen permeability, and at least onesealing layer arranged to be in contact with a surface of the at leastone barrier layer to plug at least one defect present in the barrierlayer, wherein the at least one sealing layer comprises reactivenanoparticles interacting by way of a chemical reaction with at leastone of moisture and oxygen to retard the permeation of the at least oneof moisture and oxygen through the at least one defect present in thebarrier layer, wherein the nanoparticles present in the at least onesealing layer plug the at least one defect present in the at least onebarrier layer, wherein the sealing layer is formed by conformaldeposition, wherein the conformal deposition is selected from the groupconsisting of chemical vapour deposition, spin coating, screen printing,WebFlight method, tip coating, atomic layer deposition, and pulsed laserdeposition, wherein the barrier layer comprises a material selected fromindium tin oxide (no), TiAlN, SiO₂, SiC, Si₃N₄, TiO₂, HfO₂, Y₂O₃, Ta₂O₅and Al₂O₃ and wherein a permeation rate of the barrier stack having theat least one sealing layer on the surface of the at least one barrierlayer is 10⁻³ g/m²/day or less.
 36. The barrier stack of claim 35,wherein the amount by weight of the polymeric binder present in thesealing layer is less than the amount by weight of the nanoparticlespresent in the sealing layer.
 37. The barrier stack of claim 36, whereinthe polymeric binder is between 30% and 50% of the total weight of thesealing layer.
 38. The barrier stack of claim 35, wherein the sealinglayer is a nanoparticle sealing layer.
 39. A method to manufacture anencapsulation barrier stack, comprising: providing at least one barrierlayer; and forming at least one sealing layer on a surface of the atleast one barrier layer, wherein forming the at least one sealing layercomprises conformal deposition of the at least one sealing layer overthe at least one barrier layer under vacuum or in an inert gasenvironment, the at least one barrier layer having at least one of lowmoisture and low oxygen permeability, wherein the at least one sealinglayer is arranged to be in contact with the surface of the at least onebarrier layer to plug at least one defect present in the barrier layer,wherein the at least one sealing layer comprises reactive nanoparticlesinteracting by way of a chemical reaction with at least one of moistureand oxygen to retard the permeation of the at least one of moisture andoxygen through the at least one defect present in the barrier layer,wherein the nanoparticles present in the at least one sealing layer plugthe at least one defect present in the at least one barrier layer,wherein the conformal deposition is selected from the group consistingof chemical vapour deposition, screen printing, WebFlight method, tipcoating, atomic layer deposition, and pulsed laser deposition, whereinthe barrier layer comprises a material selected from indium tin oxide(ITO), TiAlN, SiO₂, SiC, Si₃N₄, TiO₂, HfO₂, Y₂O₃, Ta₂O₅, and Al₂O₃ andwherein a permeation rate of the barrier stack having the at least onesealing layer on the surface of the at least one barrier layer is 10⁻³g/m²/day or less.
 40. An encapsulation barrier stack for encapsulatingat least one of a moisture and oxygen sensitive article, comprising: amultilayer film to be arranged on a substrate, the multilayer filmcomprising at least one barrier layer having at least one of lowmoisture and low oxygen permeability, and at least one sealing layerarranged to be in contact with a surface of the at least one barrierlayer, for plugging at least one defect present in the barrier layer,wherein the at least one sealing layer comprises reactive nanoparticlesinteracting by way of a chemical reaction with at least one of moistureand oxygen to retard the permeation of the at least one of moisture andoxygen through the at least one defect present in the barrier layer,wherein the nanoparticles present in the at least one sealing layer plugthe at least one defect present in the at least one barrier layer,wherein a shape of the nanoparticles is used to control sealing ofdefects in the at least one barrier layer, wherein the defects arestructural defects including at least one of pinholes and cracks,wherein the barrier layer comprises a material selected from indium tinoxide (ITO), TiAlN, SiO₂, SiC, Si₃N₄, TiO₂, HfO₂, Y₂O₃, Ta₂O₅ and Al₂O₃and wherein a permeation rate of the barrier stack having at least onesealing layer on the surface of the at least one barrier layer is 10⁻³g/m²/day or less.
 41. A method to manufacture an encapsulation barrierstack, comprising: forming at least one barrier layer; and forming atleast one sealing layer on a surface of the at least one barrier layer,wherein forming the at least one sealing layer comprises conformaldeposition of the at least one sealing layer over the at least onebarrier layer under vacuum or in an inert gas environment, the at leastone barrier layer having at least one of low moisture and low oxygenpermeability, wherein the at least one sealing layer is arranged to bein contact with the surface of the at least one barrier layer, to plugat least one defect present in the barrier layer, wherein the at leastone sealing layer comprises reactive nanoparticles interacting by way ofa chemical reaction with at least one of moisture and oxygen to retardthe permeation of the at least one of moisture and oxygen through the atleast one defect present in the barrier layer, wherein the nanoparticlespresent in the at least one sealing layer plug the at least one defectpresent in the at least one barrier layer, wherein the forming the atleast one sealing layer comprises adding the nanoparticles to an organicsolvent, and curing the sealing layer, wherein the barrier layercomprises a material selected from indium tin oxide (ITO), TiAlN, SiO₂,SiC, Si₃N₄, TiO₂, HfO₂, Y₂O₃, Ta₂O₅ and Al₂O₃ and wherein a permeationrate of the barrier stack having the at least one sealing layer on thesurface of the at least one barrier layer is 10⁻³ g/m²/day or less. 42.An encapsulation barrier stack for encapsulating at least one of amoisture and oxygen sensitive article, comprising: a multilayer film tobe arranged on a substrate, the multilayer film comprising at least onebarrier layer having at least one of low moisture and low oxygenpermeability, and at least one sealing layer arranged to be in contactwith a surface of the at least one barrier layer, for entirely pluggingat least one defect present in the barrier layer, wherein the at leastone sealing layer comprises reactive nanoparticles interacting by way ofa chemical reaction with at least one of moisture and oxygen to retardthe permeation of the at least one of moisture and oxygen through the atleast one defect present in the barrier layer, wherein the nanoparticlespresent in the at least one sealing layer are distributed in a sealingsolution to entirely plug the at least one defect present in the atleast one barrier layer, wherein the barrier layer comprises a materialselected from indium tin oxide (no), TiAlN, SiO₂, SiC, Si₃N₄, TiO₂,HfO₂, Y₂O₃, Ta₂O₅ and Al₂O₃ and wherein a permeation rate of the barrierstack having the at least one sealing layer on the surface of the atleast one barrier layer is 10⁻³ g/m²/day or less.